I had a further look at the toc.ncx with a hex oriented editor and it seems clear that the label for each TOC entry is being surrounded with a series of bytes that cannot be displayed.
The offending string seems the same each time :
Code:
00 00 E2 84 A1 E7 89 A2 E6 AC B0 E6 B9 A5 E2 84 A1 00
As an aside it appears that the Firefox add-on, EPUBReader, couldn't care less about this and actually shows the TOC which works perfectly. ADE and Sigil just give up at the first <null> and thus show a truncated TOC with no entries.
BobC